Spectroscopy is a general term for the process of measuring energy or intensity as a function of wavelength in a beam of light or radiation. Spectroscopy uses absorption, emission, or scattering of electromagnetic radiation by atoms, molecules or ions to qualitatively and quantitatively study physical properties and processes of matter.
A typical Raman spectrometer, for example, identifies a sample of an unknown material by measuring intensities across a spectrum of light or radiation received from the sample. A sampled spectrum is then matched against a library of known Raman spectra to identify the sample of unknown material. The sampled spectrum is matched to a known spectrum within the library using algorithms that map the correlation between the unknown spectrum and the library spectra. One example of a Raman spectrometer is disclosed in U.S. Pat. No. 7,403,281 entitled “Raman Spectrometer” and issued to Keith T. Canon et al. on Jul. 22, 2008, which is incorporated herein by reference as if fully set forth herein.
A spectrometer, for example, can disperse the light or radiation and use an array detector, such as a charge coupled device detector, to collect an array of data points that can be used to reconstruct the spectra. A laser excitation source is highly stabilized in the frequency domain so that a sampled spectrum can be precisely measured against the library of known Raman spectra.
Raman reporters or tags having known spectra can be used in a spectroscopic system. In one particular application, for example, nanoparticles tagged with specific coatings constitute Raman reporters or tags that have a very large Raman signal due to the phenomenon known as Surface Enhanced Raman Scattering (SERS). Raman reporters or tags are typically used in medical assays, brand security, and military applications. These applications differ from Raman material identification in that the sample Raman spectrum is not used to identify an unknown material. Rather, the Raman spectrum of a tag is known. In some applications, multiple tags (e.g., up to 50 tags) are used having different Raman spectra.